Conventionally, a wide-area surveillance system using a plurality of surveillance camera terminals has been used at a station, shopping center, busy streets or a like place where an unspecified number of people gather, in order to detect a person such as a suspicious individual having showed unusual behavior or a like person (hereinafter will be simply referred to as an “object person”) and track the object person thus detected. In order to reduce the cost to be incurred for construction of such a system by reducing the number of surveillance camera terminals to be used in the entire system, it has also been a practice to use surveillance camera terminals each of which is capable of changing its imaging visual field with travel of the object person, thereby increasing the surveillance area assigned to each surveillance camera terminal (see Patent Literature 1).